System and method for control of electromagnetic radiation in pecvd discharge processes

ABSTRACT

A system and method for coating a substrate with a film is described. One embodiment includes a process that provides a substrate on which to deposit a film; generates a plasma to produce radicals from a support gas; produces the radicals from the support gas; disassociates a precursor gas using the radicals; deposits material from the disassociated precursor gas on the substrate; and controls the amount of electromagnetic radiation to which the deposited material is exposed.

FIELD OF THE INVENTION

The present invention relates to plasma enhanced chemical vapordeposition (PECVD) processes. In particular, but not by way oflimitation, the present invention relates to systems and methods forcontrolling electromagnetic radiation during the PECVD process.

BACKGROUND OF THE INVENTION

The process of depositing films using PECVD is well known and has beenemployed for many years. PECVD is used in several industries to depositnon-conductive and conductive films on a variety of substrates,including glass, semiconductor wafers, and plasma display panels.

These films vary widely in quality and chemistry. With regard toquality, films made of the same material can vary widely in density andpurity. That is, depending upon the PECVD parameters, the type of PECVDsystem, and the system inputs, films can increase or decrease inquality.

In some cases, variations in film quality and chemistry areunintentional. But in other cases, film chemistry can deliberately bealtered to create films with particular properties and characteristics.For example, PECVD process parameters such as radical density, pulsingfrequency, duty cycle, gas pressure, and temperature can be varied tochange film chemistry.

As the control over these process parameters improves, new applicationsbecome available for films and film quality for existing applicationsincreases. Despite current process controls, the PECVD industrycontinues to search for new and better ways to control film chemistry.Accordingly, systems and methods are needed to more finely control filmchemistry. Similarly, new films are needed that can be produced as aresult of finely controlled film chemistry.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

A system and method for coating a substrate with a film is described.One embodiment includes a process that provides a substrate on which todeposit a film; generates a plasma to produce radicals from a supportgas; produces the radicals from the support gas; disassociates aprecursor gas using the radicals; deposits material from thedisassociated precursor gas on the substrate; and controls the amount ofelectromagnetic radiation to which the deposited material is exposed.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and a more complete understanding of thepresent invention are apparent and more readily appreciated by referenceto the following Detailed Description and to the appended claims whentaken in conjunction with the accompanying Drawings wherein:

FIG. 1 is a block diagram of a remote plasma source in accordance withconventional technology;

FIG. 2 is a diagram of a remote plasma source in accordance withconventional technology in operation;

FIG. 3 is an illustration of a dielectric film constructed in accordancewith conventional processes;

FIG. 4 is an illustration of a direct plasma source in accordance withconventional technology;

FIG. 5 is an illustration of a dielectric film constructed in accordancewith principles of one embodiment of the present invention;

FIG. 6 is an illustration of a remote plasma source with anelectromagnetic radiation assist device;

FIG. 7 is an illustration of a direct plasma source that includes aradiation assist device;

FIG. 8 is an illustration of a direct plasma source in accordance withone embodiment of the present invention;

FIG. 9 is an illustration of a thin film constructed in accordance withone embodiment of the present invention;

FIG. 10 is an illustration of a thin film constructed in accordance withanother embodiment of the present invention;

FIG. 11A illustrates a power waveform that can be used to generateadditional ultraviolet radiation;

FIG. 11B illustrates the ultraviolet radiation that results from thepower waveform of FIG. 11A;

FIG. 12A illustrates a power wave form that can be used to generateadditional ultraviolet radiation; and

FIG. 12B illustrates the ultraviolet radiation that results from thewave form of FIG. 12A.

DETAILED DESCRIPTION

Referring now to the drawings, where like or similar elements aregenerally designated with identical reference numerals throughout theseveral views, and referring in particular to FIG. 1, it is a remotePECVD system 100 in accordance with conventional technology. This systemincludes a process chamber 105, a substrate support 110, a substrate 115on which a film will be deposited, a precursor gas source 120, a gaspump 125, a plasma chamber 130, an antenna 135, a protective sheath 140,a supporting gas source 145, and a connecting neck 150 that connects theplasma chamber 130 with the process chamber 105. Remote plasma systemsof this type are generally known in the art and not described in fulldetail herein.

Referring now to FIG. 2, it shows the remote PECVD system 100 of FIG. 1in operation. This PECVD system 100 is configured to deposit adielectric layer of SiO₂ onto the substrate 115. To deposit thisdielectric layer, the precursor gas, HMDSO, is disassociated using O₃and O₁ ions. These O₃ and O₁ ions are created by exposing the supportinggas, O₂, to electrons emitted by the antenna 135 and to ion collisions.Generally, the antenna 135 is powered by an RF source, but it could alsobe driven by other power sources.

The electrons emitted from the antenna 135 causes the O₂ gas to ionizeand form a plasma 155. This plasma 155 causes a cascade reaction,thereby forming more ions and fractionalized O₂ gas (radicals). Theseradicals then travel through the neck 150 connecting the remote plasmachamber 130 to the plasma chamber 105. Once in the plasma chamber 105,the radicals collide with the HMDSO molecules, breaking them into SiOx,H, OH, etc.

For this embodiment, a perfect film would include only SiO₂. However,waste particles such as OH, H₂O and SiOH form during the disassociationand deposition process. And these particles also deposit upon thesubstrate and growing film. When the growing film is SiO₂, theseimpurities reduce its dielectric properties but may also introduceflexibility into the film. Similar changes result in other types offilms.

Most of the impurities produced during the PECVD process are actuallypumped out of the process chamber rather than deposited upon thesubstrate. However, in most processes, enough impurities deposit uponthe substrate to significantly change the film chemistry.

Those of skill in the art will understand that a remote plasma sourcecan be used for other thin films besides the dielectric SiO₂ layer. Thisprocess is shown for illustration purposes only.

Referring now to FIG. 3, it illustrates a SiO₂ film 160 produced by theremote PECVD system described in FIG. 2. This figure illustrates asubstrate layer and the film deposited thereon. Most of the thin film isformed of SiO₂. However, the film also includes certain impurities suchas OH, H₂O and SiOH. These impurities tend to slowly combine in thematrix with un-decomposed materials from the precursor,fractionalization processes materials and also unsatisfied bonds in thematrix increasing the films density, this results in increased filmstress that lead to cracking and delamination as the film ages.Moreover, the film does not have a uniform density. That is, thedeposited material is not deposited evenly and leaves gaps. Moreover, asthe film cools, some of the H₂O molecules eventually escape, leavinggaps where the H₂O molecules were originally located.

These types of flaws in thin films are found in nearly all filmchemistries and are not limited to SiO₂ dielectrics. And although thesefilms are functional for some purposes, these flaws limit the film'sability and life span in many instances. For example, these impuritiesand gaps cause thin films to crack and reduce their desired electricalproperties.

In some instances, films may actually benefit from a carefully addedamount of impurities. But this process of adding impurities must becarefully controlled or the film quality will suffer significantly.

Referring now to FIG. 4, it illustrates a direct PECVD system 170 inaccordance with conventional technology. In this type of PECVD system,the plasma chamber and process chambers are combined. Otherwise, thedirect PECVD system works similarly to the remote PECVD system.

This embodiment of a conventional PECVD system includes a processchamber 175, an antenna 180, a dielectric sheath 185, a supporting gassupply 190, a precursor gas supply 195, and a substrate 200. Althoughnot shown, this system could also include a substrate support. Again,this type of PECVD system is well known in the art and not described ingreat detail herein.

Although this PECVD system should work almost identically to the remotePECVD system shown in FIG. 1, it has been discovered that, for certainfilm chemistries, the direct PECVD system produces a somewhat higherquality film than does the remote PECVD system. For example, FIG. 5illustrates a dielectric film 205 produced by a direct PECVD system.While this film still includes impurities and gaps that reduce theoverall quality of the film, the number of impurities and gaps isdecreased.

It was recently discovered that part of the reason for this increase infilm quality was due to electromagnetic radiation, and in particularultraviolet radiation, radiated outward from the plasma formed aroundthe antenna. In a remote PECVD system, the electromagnetic radiation wasblocked from reaching the substrate and the growing film. But in thedirect PECVD system, the radiation from the plasma could directlybombard the substrate and the growing film. This bombardment wasdiscovered to significantly affect the chemistry of the growing film. Insome instances, the electromagnetic radiation bombardment enhanced thequality of the film. However, in other cases, the electromagneticradiation bombardment could actually disrupt the growth of the film.

As previously discussed, the PECVD industry is always searching for newand better ways to control the PECVD process and more finely tune thechemistry of the deposited films. And conventionally, the PECVD industrycontrolled process parameters such as radical density, pulsingfrequency, duty cycle, gas pressure and temperature. In accordance withembodiments of the present invention, the additional process parameterof electromagnetic radiation can also be controlled.

By controlling the amount of electromagnetic radiation, including UVradiation, to which the growing film is exposed, film chemistry can bemore finely controlled. Moreover, the substrate can be preconditioned bycontrolling the amount of electromagnetic radiation to which thesubstrate is exposed prior to depositing the film. In both instances,the amount of electromagnetic radiation can be significantly and quicklyvaried during the course of film production. Alternatively, the amountof electromagnetic radiation can be set for a desired film chemistry.This ability to vary electromagnetic radiation during the filmproduction allows film chemistry to be finely controlled and changed asthe film is grown.

Referring now to FIG. 6, this is one embodiment of a PECVD system 210that includes electromagnetic radiation control. This system is a remoteplasma system similar to the system shown in FIG. 1. This systemincludes the plasma chamber 130 and the process chamber 105 separated bya connecting neck 150. Typically, this type of system blockselectromagnetic radiation produced by the plasma from reaching thesubstrate. But this system uses a radiation assist device 215 added tothe process chamber to introduce radiation to the growing film.

In one embodiment, this radiation assist device 215 is an ultravioletsource that is controlled by a computer or manually by a user. The UVsource output could be linked to any of the process parameters commonlyused to control film quality. For example, the UV source could be linkedto radical density so that the UV source is at a high output level whenradical density is at its lowest point and UV could be at its lowestpoint when radical density is at its highest point. Those of skill inthe art could determine how to adjust the process parameters and the UVoutput to achieve their unique, desired film chemistries.

FIG. 7 illustrates a direct plasma source that includes a radiationassist device 225. This direct plasma system is similar to the systemshown in FIG. 4. It includes the process chamber 230, the antenna 235,the dielectric sheath 240 protecting the antenna, the substrate support245, the substrate 250, a supporting gas supply 255, a precursor gassupply 260, and an exhaust pump 270.

In this embodiment it is assumed that the electromagnetic radiationradiated from the plasma around the antenna 235 is not sufficient toachieve the film properties desired. Accordingly, an assist device 225is added to provide extra electromagnetic radiation as needed. Thiselectromagnetic radiation assist device 225 could also be manuallycontrolled or computer controlled and timed to operate with otherconventional process parameters.

FIG. 8 illustrates a portion of a direct PECVD system 275 in accordancewith the present invention. This diagram illustrates a cutaway of theprocess chamber 280. In particular, it illustrates the process chamberwalls 280, the antenna 285, the dielectric sheath 290 protecting theantenna, the substrate support 295, and the substrate 300. Thisembodiment also illustrates a radiation shield 305 with variableshutters 310 to restrict apertures in the shield. The general operationof a process chamber and a PECVD systems—not including the radiationshield—is known in the art and not described further.

This embodiment assumes that the electromagnetic radiation produced bythe plasma surrounding the antenna 285 is sufficient to sufficientlyalter film chemistry. In fact, this embodiment assumes that at times theelectromagnetic radiation produced by the plasma may be more than isneeded to adequately alter film chemistry. Accordingly, the shutters 310in this embodiment can be opened, restricted, or closed as the processparameters demand. The shutters 310 are designed to block the passage ofelectromagnetic radiation. As with the previously described radiationsources, the shutters can be linked to other process parameter controlsto finally control film chemistry. Shutters can include any device thatrestricts electromagnetic radiation, including UV radiations.

FIGS. 9 and 10 illustrate two film chemistries that can be produced bycontrolling the amount of electromagnetic radiation that bombards thegrowing film. In FIG. 9, the electromagnetic radiation is increased asthe film 315 is grown. For example, the shutters shown in FIG. 8 couldbe slowly opened as the film 315 is grown. The resulting film chemistrybecomes more dense as the film grows outward. For a dielectric layerformed of SiO₂, this type of increasing density film results in anorgano-silicon layer nearest the substrate and a dense SiO₂ layer on theouter portions of the film. This type of film chemistry is desirable insome cases so that the film adheres to the underlying substrateadequately.

FIG. 10 illustrates another type of Film 320 that can be generated bycontrolling the amount of radiation that bombards the film. In this film320, the film density varies from less dense to dense, back to lessdense. This type of chemistry produces desirable electrical propertiesin certain instances.

In some instances, control of electromagnetic radiation alone canproduce the desired film chemistries. But as previously described, inother instances, the electromagnetic radiation is controlled inconjunction with other process parameters such as radical density, powermodulation, duty cycle, pulsing frequency, pulse shape, gas pressure,and radical density. In particular, as previously described, one novelmethod of using UV control involves linking the amount of UV at the filmto the radical density.

For example, if a SiO₂ dielectric layer is being deposited, the UV couldbe linked to the density of O₁ and O₃ radicals at a particular point intime. As the radical density decreases, the amount of UV could beincreased to prepare the surface of the film as the deposition ratelowers, and as the radical density increases, the UV could be reduced toallow more material to be deposited unencumbered by added energysources.

Referring now to FIGS. 11A and 11B, they illustrates a power waveformthat can be used to generate additional ultraviolet radiation.Generally, the PECVD process is driven by applying microwave or RFfrequency power signals to the antenna within the process chamber. Inaccordance with one embodiment of the present invention, the powersignal can be modified to generate more or less ultraviolet radiation.In this embodiment, the power applied to the PECVD process is initiallyspiked. Although the spike adds little to the overall power delivered tothe PECVD process, the power spike generates significant amounts ofadditional ultraviolet radiation. This additional ultraviolet radiationis illustrated in FIG. 11B.

Notably, embodiments that use power waveform contouring to control theamount of ultraviolet radiation need not include any type of radiationshield. Although some embodiments of the present invention can alsoinclude a radiation shield.

FIGS. 12A and 12B, they illustrate alternate waveforms used to generateadditional ultraviolet radiation. In this embodiment, the power isspiked twice during a single pulse. These spikes do little to theoverall power delivered to the PECVD process, but significantly increasethe amount of ultraviolet radiation produced.

Additionally, controlling the contour of the pulse shape also enablescontrol over the wavelength of the produced ultraviolet radiation. Andin some embodiments, the wavelength is controlled independently of theamount of ultraviolet radiation produced.

In conclusion, the present invention provides, among other things, asystem and method for PECVD and controlling the PECVD process. Thoseskilled in the art can readily recognize that numerous variations andsubstitutions may be made in the invention, its use and itsconfiguration to achieve substantially the same results as achieved bythe embodiments described herein. Accordingly, there is no intention tolimit the invention to the disclosed exemplary forms. Many variations,modifications and alternative constructions fall within the scope andspirit of the disclosed invention as expressed in the claims.

1. A method for coating a substrate with a film, the method comprising:providing a substrate on which to deposit a film; generating a plasma toproduce radicals from a support gas; producing the radicals from thesupport gas; disassociating a precursor gas using the radicals;depositing material from the disassociated precursor gas on thesubstrate; and controlling the amount of electromagnetic radiation towhich the deposited material is exposed.
 2. The method of claim 1,wherein controlling the amount of electromagnetic radiation to which thedeposited material is exposed comprises: blocking ultraviolet radiationemitted by the plasma.
 3. The method of claim 1, wherein controlling theamount of electromagnetic radiation to which the deposited material isexposed comprises: reducing an aperture opening between the plasma andthe deposited material.
 4. The method of claim 1, wherein controllingthe amount of electromagnetic radiation to which the deposited materialis exposed comprises: increasing ultraviolet radiation generated.
 5. Themethod of claim 1, wherein generating a plasma to produce radicals froma support gas comprises: providing a power signal to generate theplasma.
 6. The method of claim 5, wherein providing a power signal togenerate the plasma comprises: spiking the power signal to therebyincrease the amount of ultraviolet radiation.
 7. The method of claim 6,wherein spiking the power signal to thereby increase the amount ofultraviolet radiation comprises: controlling the timing of spiking thepower signal to thereby control the increase in the amount ofultraviolet radiation.
 8. The method of claim 1, wherein providing apower signal to generate the plasma comprises: varying the power signalto thereby increase the amount of ultraviolet radiation.
 9. The methodof claim 1, wherein providing a power signal to generate the plasmacomprises: varying the power signal to thereby vary the wavelength ofthe ultraviolet radiation.
 10. The method of claim 1, whereincontrolling the amount of electromagnetic radiation to which thedeposited material is exposed comprises: varying the amount ofultraviolet radiation to which the deposited material is exposed inaccordance with the density of radicals.
 11. The method of claim 10,wherein varying the amount of ultraviolet radiation to which thedeposited material is exposed comprises: increasing the amount ofultraviolet radiation to which the deposited material is exposed whenthe density of radicals is reduced.
 12. The method of claim 10, whereinvarying the amount of ultraviolet radiation to which the depositedmaterial is exposed comprises: decreasing the amount of ultravioletradiation to which the deposited material is exposed when the density ofradicals is increased.
 13. The method of claim 8, wherein controllingthe amount of electromagnetic radiation to which the deposited materialis exposed comprises: varying the amount of ultraviolet radiation towhich the deposited material is exposed in accordance with variations toa power signal used to produce the plasma.
 14. A PECVD systemcomprising: a plasma chamber; an antenna; a substrate support; aelectromagnetic radiation restrictor positioned between the antenna andthe substrate support, the restrictor having a controllable aperture;and a controller configured to control the controllable aperture. 15.The PECVD system of claim 14, wherein the controller comprises: acomputer configured to vary the size of the aperture according to atleast one PECVD process parameter.
 16. The PECVD system of claim 14,wherein the controller comprises: a computer configured to vary the sizeof the aperture according to a density of radicals produced in theplasma chamber.
 17. The PECVD system of claim 14, wherein the controllercomprises: a computer configured to vary the size of the apertureaccording to variations in a power signal applied to the antenna.
 18. Amethod of producing a film, the method comprising: initiating a PECVDprocess to deposit a film on a substrate; and varying the amount ofultraviolet radiation to which the film is exposed during growth. 19.The method of claim 18, wherein varying the amount of ultravioletradiation to which the film is exposed during growth comprises:mechanically varying the amount of ultraviolet radiation to which thefilm is exposed during growth.
 20. The method of claim 18, whereinvarying the amount of ultraviolet radiation to which the film is exposedduring growth comprises and wherein a plasma used during the PECVDprocess generates a first amount ultraviolet radiation comprises:blocking a first portion of the first amount of ultraviolet radiationfrom reaching the film.
 21. The method of claim 20, wherein varying theamount of ultraviolet radiation to which the film is exposed duringgrowth comprises and wherein a plasma used during the PECVD processgenerates a first amount ultraviolet radiation: blocking less than thefirst portion of the first amount of ultraviolet radiation blocked fromreaching the film.
 22. The method of claim 18, wherein varying theamount of ultraviolet radiation to which the film is exposed duringgrowth comprises: varying the amount of ultraviolet radiation to whichthe film is exposed during growth by contouring a power waveform used todrive the PECVD process.
 23. A method of producing a film, the methodcomprising: initiating a PECVD process to deposit a film on a substrate;generating ultraviolet radiation, wherein the film is exposed to theultraviolet radiation; varying the wavelength of the ultravioletradiation.
 24. The method of claim 23, wherein varying the wavelength ofthe ultraviolet radiation comprises: contouring a power waveform used todrive the PECVD process.